The controlled electrolytic generation of gases is useful to convert chemical to mechanical energy in a variety of applications. For example, a variety of lubricant or fluid delivery systems driven by the electrolytic generation of a gas are known. For example, U.S. Pat. No. 4,023,648 to Orlitzky et al. (1977) shows a lubricant applicator driven by gas generated in an electrochemical cell and provides a method for the electrochemical generation of hydrogen gas.
Fluid dispensers driven by electrochemically generated gases, and other electrochemical transducers may often be used in circumstances which give rise to special operational requirements. Typically, components of any electrolytic cell used in such an application must be stable over time and over a range of temperatures. In such devices, it is undesirable to have highly reactive gases generated, such as hydrogen or oxygen. Once the circuits are closed to initiate electrolytic gas generation, it is desirable to have relatively fast electrode reactions with low overpotential (i.e. a small difference between the electrode potential under electrolysis conditions and the thermodynamic value of the electrode potential in the absence of electrolysis), small concentration polarisation of solutes across the cell (i.e. rapid diffusion of reactants to the electrode surfaces), and small separator resistance effects (i.e. little resistance caused by solid separators within the cell. It is also desirable to produce gases from a small amount of material, i.e. to have efficient gas generation and high stoichiometric coefficients for gaseous reaction products.
Hydrogen and oxygen gases are used in a variety of known electrochemical gas generators. One disadvantage of such systems is the chemical reactivity of those gases. Another disadvantage of hydrogen in particular is that it diffuses relatively rapidly through a variety of polymeric barriers that might otherwise be used to contain the electrolytically generated gas in a mechanical transducer, such as a fluid dispenser.
Nitrogen is a relatively inert gas that may usefully be produced by electrolytic reactions to provide controlled amounts of gas. However, existing methods for the electrolytic generation of nitrogen suffer from a number of disadvantages.
U.S. Pat. No. 5,567,287 issued to Joshi et al. (1996) discloses a solid state electrochemical nitrogen gas generator for fluid dispensing applications. Nitrogen is produced in that system by the electro-oxidation of a decomposable solid material of the generic formula A.sub.x N.sub.y in a divided electrochemical cell, where "A" is an alkali metal such as sodium or lithium, "N" is nitrogen, x is 1 to 3 and y is 1 to 3. Example compounds disclosed therein include LiN.sub.3 (lithium nitride) and NaN.sub.3 (sodium azide). The azide half cell reaction in such a system (reaction 1) may however be slow, in part because of the high overpotential required for the electro-oxidation of azide. EQU 2N.sup.3-.fwdarw.3N.sub.2 +2e.sup.- (1)
To overcome the problem of the sluggish kinetics of the azide half-cell, additives such as thiocyanate may be used to catalyse the iodine mediated formation of nitrogen from azides, as in reactions 2 and 3: EQU 2I.sup.-.fwdarw.I.sub.2 +2e.sup.- (2) EQU I.sub.2 +2N.sub.3.sup.- {character pullout}2I.sup.- +3N.sub.2 (3)
However, such systems suffer from the disadvantages that azides are toxic and the thiocyanate salt catalysts are also toxic. The presence of toxic compounds may make it difficult to dispose of a device which generates nitrogen gas from azides.